Machines that make use of lead-in wires to lay out the circuits, such as an amplifier and speaker for a hi-fi equipment, are connected to each other by connection wires formed of a pair of L- and R-signal wires. The connection between these machines are normally achieved by stripping the tips of the lead-in wires, and then connecting the stripped tips to the connection members known as lever type connection plugs 103 mounted on the terminal plates 101 of the machines (refer to FIG. 10).
In the lever type connection plug 103, the lever 105 can resist the torque of the spiral spring 107 to rotate clockwise, so that the end of a stripped lead-in wire 109 can be inserted into the hole 111. After this, the lever 105 resumes its original position, and the lead-in wire 109 is moved to locate in between the contact member 113 of the lever 105 and the contact member 117 located within the housing 115 of the connection plug 103, to provide electrical connection to the contact member 117 of the machine side.
For the recent hi-fi equipments, besides the two-channels input, there are also multiple signal inputs of four-channels and six-channels. Under the circumstances, for each channel, it is necessary to connect the lead-in wires 109 composed of two signal lines. Therefore, as shown in FIG. 11, multiple lever type connection plugs 103 are arranged on the terminal plate 101 at the back of the machine.
However, it is unesthetic to locate the connection portion of the lead-in wire 109 on the surface of the machine. Therefore, normally the terminal plates 101 are located on the rear of the machine. Since it is required to perform lay out of the wire at the rear of the machine where the user is difficult to view, it is difficult to perform the lay out. Furthermore, since the diameter of the lead-in wire 109 ranges from 0.76 to 1.27 mm., it may be not possible to securely retain all the lead-in wires 109 of various diameters to perform electrical connection.
To overcome the above defects, the applicant provides the plug for connecting electrical wires 200 as disclosed Japanese Patent Application No. 2002-75485 (see FIGS. 12 to 14).
With reference to the plug 200, the lead-in wires 3 composed of a pair of signal lines 3 are inserted into the respective openings 211, 211 of the rear portion of the housing 210. The housing 210 with the lead-in wires 5, 7 connected thereto is inserted into the slot 139 of socket 127 located on the terminal plate 137 of the machine rear surface.
The shape of the housing 210 corresponds to the cross-sectional shape of the slot 139. A recess 212 is formed at one side of the housing 210, and is adapted to engage with the rib 141 formed on an inner face of the slot 139. Therefore, the plug 200 is insertable only when the recess 212 engages the rib 141, and thus accidental insertion of the plug may be avoided.
Wire connecting head 220 suitable for resiliently connecting with the machine side terminals (plug-in terminals) 131 is mounted in the housing 210. The wire connecting heads 220 correspond to the pair of lead-in wires 5, 7, and are stacked in the housing 220 (see FIG. 12).
A zigzagging plate-like spring piece 223 is integrally formed on one side of the wire connecting head 220. A recess 225 is formed on the spring piece 223, and is engageable with the urging portion 231 of the rotating lever 230.
The rotating lever 230 is in the shape of an inverted “L.” By rotating the operating portion 232 extending from the housing 210, the spring piece 223 is urged towards the direction of the lead-in wires 5, 7 by the front end of the urging portion 231.
As shown in FIG. 14, in the course of rotation, the urging portion 231 moves to engage with the recess 225 of the spring piece 232. At this instant, the stripped portions 250 of the lead-in wires 5, 7 are clamped to secure in the inner wall face of the housing 210 by the front end of the spring piece 223. Therefore, the lead-in wires 5, 7 are electrically connected to the wire connecting head 220, and can be electrically connected to the machine side terminals 131 via the wire connecting head 220.
In this kind of connection plug 200, the plug 200 is inserted into the slot 139 of socket 127 located on the machine, and the lead-in wires 5, 7 are connected to the machine side terminals 131. Therefore, the connection can be easily achieved even at the machine rear side. The plug 200 is well adapted for lead-in wires 5, 7 of various diameters.
[Problems to be Solved]
In the connection plug 200 shown in FIGS. 12 to 14, the front end of the spring piece 223 is pressed to secure the lead-in wires 5, 7. Although the lead-in wires 5, 7 will not be loosen easily, the retaining force for such connection plug 200 is insufficient.
In other words, when the user removes the plug 200 from the socket 127, the lead-in wires 5, 7 may be accidentally pulled. If the force for retaining the lead-in wires 5, 7 does not exceed the force for removing the plug 200 from the socket 127, for example 5 kg, the lead-in wires 5, 7 may be removed before the plug 200 is removed from the socket 127.
The above-mentioned known plug 200 which retains the lead-in wires 5, 7 by clamping only is limited in its retaining force, and thus has the above defect.
Further, since the stripped portion 250 of the lead-in wires 5, 7 are clamped by the sharp edges of the front end of the spring piece 223, the stripped portion 250 apt to be easily broken partially, and the lead-in wires will no longer function.
The broken portion of the stripped portion 250 may remain in the housing 210 or socket 127, and may result in poor insulation.
The location of the front end of the spring piece 223 urging against the lead-in wires 5, 7 may vary due to the insertion condition of the lead-in wires 5, 7. Therefore, the flexure amount of the spring piece 223 may vary, and will result in the instability of the contact pressure of the lead-in wires 5, 7. Consequently, the contact resistance will vary and the electrical connection having a predetermined value may not be attained.
The present invention is intended to overcome the above drawbacks, and provides a socket connector for electrical wires having sufficient retention force, which may prevent the wires from breaking and to provide a contact resistance of predetermined value.